Method of sealing off water bearing formations



Patented May 14, 1940 UNITED STATES PATENT OFFICE METHOD or SEALING our ws'raa anama Foam'rroNs Franklin A. Bent, Albert G. Loomis, and Howard C. Lawton, Berkeley, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application February 19, 1938,

, Serial No. 191,402

The method of the. present invention consists in treating the water bearing layers with hydrofiuosilicic, hydrofluotitanic, hydrofluozirconic and hydrofluoferric acids and with their water-soluble organic or inorganic salts. For example,

11 Claims.

the well, forced into the layer to be sealed off,

and caused to deposit a sealing precipitate in the pores of said layer by reaction with .a second solution introduced therelnto, or with certain 15 salts naturally present in the formation waters. In cases where it is desired to effect a selective shut-off of a water layer closely adjacent oil bearing sands, a method involving the use of two treating solutions should be avoided, since a portion of the treating liquids will often penetrate into the oil layer and form by inter-reaction an undesirable precipitate within the latter. In such cases, therefore, a method involving the use of a single chemical capable of forming a precipitate by reaction with the natural formation waters should bepreferred.

In practice, however, such methods meet with considerable difliculties. since the bulk of the compounds dissolved in natural oil-field waters or brines consist of sodium chloride, which does not readily form precipitates. The precipitatable compounds of formation waters are therefore chiefly limited to calcium and magnesium salts, which usually occur only in low concentrations. Since the effectiveness of a water shut-ofl. de-

t pends largely on the amount and the nature of the precipitate formed within the pores of the formation, such methods very often give unsatisfactory results.

,It is, therefore, the object of this invention to provide a method for treating water formations by forcing thereinto a treating agent capable of reacting with the water-soluble alkali compounds, chiefly sodium chloride, commonly present in the ground waters, to give a water-insoluble alkali salt precipitate in amounts sumcient for effectively plugging or sealing off said forl'na- .tions.

It is a further object ofthis invention to provide a process whereby the nature of the precipi tate formed, and the time necessary for its formation, may be controlled by means of an additional treatment in such a manner as to secure the placement of a particularly effective seal well 55 back in the strata to be sealed oil.

metallic fluosilicates, that is, metallic salts of hydrofluosilicic acid are soluble in water with the exceptio barium.

n of those of the'alkali metals and of Sodium, potassium and barium fluosilicates have solubilities of 0.65, 0.12, and 0.026 of 1% at 17.5", respectively, and may be considered as water-insoluble for the purposes of this invention Likewise, certain organic salts of hydrofluosili'cic acid, such as the amine salts, for example,

aniline hydrofluosilicate,

or dianiline hydrofluosilicate, toluidine xylidine hydro'fluosilicate,

phenylene-diamine hydrofluosilicate, methyl aniline hydrofluosilicate, diphenylamine hydrofluosilicate,

dimethyl aniline hydrofluosilicate, etc..

are sufficiently water-soluble to be applicable for the present process.

In applying the treatment of the present invention bearing to an oil-well in order to seal off waterformations, the following procedure may be followed:

The well.is first preferably filled with oil, and

a desire metallic d amount of an aqueous solution of a fluosilicate, for example, the calcium,

magnesium, lead, or iron salt of hydrofluosilicic acid, or

a water-soluble organic salt, such as dianiline hydrofluosilicate, is then introduced into the well through the tubing or casing, and is forced into the formation by pumping down another charge of oil, water, or brine, or by applying pressure to the well in any other known manner. The treating solution will diffuse into the formation water or brine, forming by reaction with the alkali salts, chiefly sodium chloride, dissolved therein,

a water-insoluble precipitate,

ions in any significant concentrations, these strata are not affected by the treatment, and 'a' preferential or selective shut-oil? of the water layers is The w eflected. ell can then be produced by releasing the pressure in order to flush out that portion of the treating solution which may have flowed. into the oil horizons, and, if desired, a charge of a second treating solution, such as ammonium hydroxide, may be forced into the formation in the manner described above. A second reaction will take place with the sodium fiuosilicate precipitated during the first treatment, with the formation of silicic acid and of ammonium fluoride, the latter reacting further with the calcium and magnesium ions of the brine, which may have been naturally present therein, or may have been added thereto in the form of magnesium or calcium fiuosilicate during the first treatment. Instead of ammonium hydroxide, sodium or potassium hydroxides may equally Well be used, care being taken to use slightly smaller quantities of these substances than the stoichiometric or theoretical quantities required to form silicic acid. If this condition is fulfilled, the formation of watersoluble alkali silicate is prevented, and the use of caustic alkalis, NaOH or KOH, will be as effective as the use of ammonium hydroxide, as shown by the following equations:

The final precipitate, consisting of a mixture of silicic acid and calcium fluoride forms an effective seal deep within the formation, since the reaction of the alkali hydroxide with sodium fiuosilicate proceeds at a relatively slow rate and permits a deep penetration of the treating liquids into the ground strata, before the latter became sealed by the precipitate formed. In order to intensify this effect, and to delay still further the interaction between the two treating agents, it may sometimes be desirable to introduce into the well and to force into the formation a charge of a neutral material, such as oil or fresh water, between the charges of the water-soluble fiuosilicate and of the caustic alkali.

Instead of the water-soluble fluosilicates, it is possible to treat briny formations directly with an aqueous solution of hydrofluosilicic acid, in which case the flow. of the treating agent should preferably be directed toward said formations by means of packers or double-packers, in a manner known to the art. This treatment, when applied to formations saturated with brines of a high sodium chloride concentration, or when followed by a caustic alkali treatment, results in the formation of a plug of silicic acid, or of silicic acid and calcium fluoride as described before. Any mixture of hydfiifluosilicic acid with one of its water-soluble metallic salts canlikewise be used.

Although the process described above is especially suitable for sealing off brine or waterbearing formations, it can also be advantageously applied for plugging formations of any other type, for example gas-bearing formations, whereby excessive amounts of gases are prevented from entering a well. In such case, the charge of the hydrofluosilicic acid or of one of its water-soluble metallic salts is forced into a gas-bearing sand, and is followed or preceded by a charge of brine, or of any other salt solution, such as a watersoluble alkali silicate, for example, sodium silicate or metasilicate, potassium silicate or tetrasilioate, to form an insoluble alkali fiuosilicate and a water-insoluble metallic silicate, as shown by th following equation:

This treatment may be followed by a treatment with an alkali hydroxide, as shown before. In a similar way, the process of the present invention may be used for sealing off or decreasing the permeability of any desired ground formation. Thus, it may have a practical application in building canals, sluices, ordykes in porous soil, where it is desirable to stop the percolation of water through the sand, or in constructing landing piers, tunnels, etc., in ground formations which are not sufiiciently impervious to fluid flow. The process is economically attractive in such cases because both the metallic fiuosilicate and sodium chloride solutions are readily and cheaply available materials.

We claim as our invention:

1. In the process of decreasing the permeability of a porous formation, the steps of introducing into such formation a treating solution capable of liberating fluosilicic ions and reacting said solution within said formation with a watersoluble alkali salt, whereby a water-insoluble alkali fiuosilicate is formed in the pores of said formation.

2. In the process of decreasing the permeability of a porous formation, the steps of introducing into said formation an aqueous solution of hydrofluosilicic acid and reacting said solution within said formation with a water-soluble alkali salt whereby a water-insoluble alkali fiuosilicate is formed in the pores of said formation.

3. In the process of decreasing the permeability of a porous formation, the steps of introducing into said formation an aqueous solution of a water-soluble metallic fiuosilicate, and reacting said solution within said formation with a watersoluble alkali salt, whereby a water-insoluble alkali fiuosilicate is formed in the pores of said formation,

5. In the process of decreasing the permeability of a porous formation, the steps of introducing into said formation an aqueous solution of a water-soluble organic salt of hydrofluosilicic acid, and reacting said solution within said formation with a water-soluble alkali salt, whereby a waterinsoluble alkali fiuosilicate is formed in the pores of said formation.

6. In the process of decreasing the permeability of a. porous formation, the steps of introducing into said formation an aqueous solution of a water-soluble amine salt of hydrofluosilicic acid,

with a water-soluble alkali salt, whereby a water-insoluble fiuosilicate is formed in the pores of said formation.

'7. In the process of decreasing the permeability of a porous formation, the steps of introducing into said formation an aqueous solution of a water-soluble metallic fiuosilicate, and reacting said solution within said formation with a water-soluble alkali silicate, whereby a water-insoluble alkali fiuosilicate and a water-insoluble metallic silicate are formed in the pores of the formation.

8. In the process of sealing off brine-bearing formations traversed by a well, the stepsof introducing into the well and forcing into said formation a treating solution comprising hydrofluosilicic acid, allowing said solution to form a water-insoluble alkali fluosilicate within said formation by reaction with the alkali salts dissolved in the formation brine, forcing into said formation a second treating solution comprising an alkali hydroxide, and allowing the second solution to react with the products of the first reaction to form a water-insoluble metallic fluoride.

9. In the process of sealing off brine-bearing formations traversed by a well, the steps of introducing into the Well and forcing into said formation a treating solution comprising a watersoluble fluosilicate, allowing said solution to form a water-insoluble alkali fiuosilicate within said formation by reaction with the alkali salts dissolved in the formation brine, forclng'into said formation a second treating solution comprising an alkali hydroxide, and allowing the second solution to react with the products of the first rcaction to form a water-insoluble metallic fluoride.

10. In a process for solidifying porous ground, the steps of introducing thereinto an aqueous solution of a water-soluble metallic fluosilicate and an aqueous solution of a water-soluble alkali salt, whereby a Water insoluble alkali fluosilicate is formed in the pores of the ground by a reaction between said solutions.

11. In the process of decreasing the permeability of a porous formation, the steps of introducing into said formation an aqueous solution of a water-soluble metallic fluosilicate, and reacting said solution within said formation with a watersoluble sodium salt, whereby the waterinsoluble sodium fluosilicate is formed in the pores of said formation.

FRANKLIN A. BENT. ALBERT G. LOOMIS. HOWARD C. LAW'I'ON. 

